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Author Topic: ALS-600 problem : loud "hum" in output  (Read 13398 times)
KE3WD
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« Reply #15 on: August 22, 2010, 04:22:34 PM »

Well, we're on the same page then, Tom. 

It is amazing how almost any information given gets turned all around on the internet. 



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N3OQD
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Posts: 104




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« Reply #16 on: August 23, 2010, 11:10:30 AM »

Yes, thinking about this more carefully, Tom is correct.  Unlike FM and AM, merely dead keying a radio in SSB mode has no modulation of its own.  So while a dead key from an AM or FM transmission would be polluted by A/C ripple, SSB without any audio of its own (dead key that is) cannot.  The A/C ripple has to ride on SOMETHING in order to be on a SSB transmission.  Hence the garbling effect of voice on SSB due to ripple that Tom has discribed.  The A/C hum "rides" the audio modulation of SSB in the absence of a continuous carrier.  If say there is a ground fault in the microphone circuit somewhere (like my Yaesu FT-450 did last year), then A/C "like" hum can be introduced to the final transmission via dead key with no audio present in the room.  The audio being relativly clear but with a distinct hum in the background.  This type of hum tonal quality would be identical to a guitarist pulling the plug from his audio amp.  Since I have worked on audio equipment over the years, I can quickly recognise its unique sound. 
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W6GF
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« Reply #17 on: August 27, 2010, 10:47:53 PM »

Before doing anything else, key the amp WITHOUT the transceiver connected.  If there is still hum your amp's power supply is at fault, if no hum there is a problem with the transceiver to amp connection.

George, W6GF

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AD5X
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« Reply #18 on: August 28, 2010, 04:20:25 AM »

Before doing anything else, key the amp WITHOUT the transceiver connected.  If there is still hum your amp's power supply is at fault, if no hum there is a problem with the transceiver to amp connection.

George, W6GF

Without a driving signal source, at what frequency would you listen for the hum?  As Tom stated, listen for ripple on a CW signal to determine if the power supply is the problem.

Phil - AD5X
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W8JI
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« Reply #19 on: August 28, 2010, 06:34:09 PM »

Before doing anything else, key the amp WITHOUT the transceiver connected.  If there is still hum your amp's power supply is at fault, if no hum there is a problem with the transceiver to amp connection.

George, W6GF

Without a driving signal source, at what frequency would you listen for the hum?  As Tom stated, listen for ripple on a CW signal to determine if the power supply is the problem.

Phil - AD5X


See how difficult it is to stay on task. :-)  We cannot test a power supply for hum by turning a linear amp on without RF drive and listening, just as we cannot test it in the SSB mode with no audio input.

The only correct way to listen for power supply hum is on CW or some carrier mode with no modulation of the carrier, and listening for hum on what should be a clean carrier.

The reason I wanted him to try it on SSB was the most common cause of hum is placing the PS near a dynamic microphone.

He has not answered any questions related to meaningful tests.

The most likely cause of the hum is not reading the manual, which cautions about power supply placement. Placing the power supply near something sensitive to magnetic flux in the radio, or the external audio devices, can cause some nasty hum. This is because the supply has a choke input that uses a swinging choke with an air gap.

We may never know what the problem really was.

73 Tom
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